Valves exist in a wide variety of forms and sizes, serving a multitude of purposes, handling the flow of materials whose characteristics range from light gases to heavy slurries and near-solids. Valves can be configured as shut-off valves so as to be operable in either of two states, i.e., completely opened and completely closed. Alternatively, the valves can be proportional control valves so that the valve can be moved though positions between fully closed and fully opened positions so that the flow through the valve can be controlled depending on how much the valve is opened. Valves can be a normally-opened valve in which case the valve is fully opened in the absence of the application of a control signal, or a normally-closed valve in which case the valve is fully closed in the absence of the application of a control signal. Proportional control valves which are capable of responding quickly to control flows with precision and with little electrical power, are of special interest in certain industrial processing, such as flow control of gases and vapors in semiconductor and integrated-circuit manufacture. Mass flow controllers, for example, are widely used in controlling the delivery of process gases in semiconductor manufacturing. Such controllers require accurate control valves so as to deliver very precise amounts of gases during process runs.
Many commercially available mass flow controllers tend to use solenoid valves because solenoid valves are accurate and reliable. Solenoid valves usually each include a valve plunger in the form of plug that moves into and out of contact with a valve seat in response to the application of current to a solenoid coil, which in turn creates flux through a magnetic circuit so as to create an electromagnetic force (emf) on an armature that moves the plug. Because the emf force can be applied to the armature in only one direction, the solenoid valve includes a spring to move the plug in the other direction when the emf force is reduced or removed. Solenoid valves have dominated the designs of mass flow controllers because of their simplicity, low cost and fast response.
Solenoid valves have been designed with a pressure balancing feature, which is particularly useful in neutralizing the forces due to pressure of the gas within the valve when applying the necessary control forces to overcome frictional forces in order to accurately control flow through broad-area flow passages, particularly when opening the valve from a normally closed state. For an example of a pressure-balanced, solenoid proportional control valve designed to reduce these adverse influences on valve performance see U.S. Pat. No. 4,796,854 (Ewing) assigned to MKS Instruments, Inc. of Andover, Mass., U.S.A.
So-called pilot valves have two valve structures coupled together, with one typically being a smaller valve that is used to control the second, larger valve. Pilot valves typically have been used in high-pressure and/or high flow rate (Q) applications. FIG. 1 illustrates a prior art pilot valve 100 in two operational conditions, shown in A and B.
Pilot valve 100 includes a pilot orifice 102 that is opened and closed by way of a solenoid 104 moving a plunger 106, which may be controlled by an external command/signal, e.g., a user using a computer or other device. In operation, the plunger 106 acts on the pilot orifice 102 to close or open it, depending upon whether the solenoid 104 is energized or de-energized, thus permitting pressurization or release of pressure in the associated pilot chamber 110. The pilot valve operates to control a “piloted” valve, which is equipped with a diaphragm 112 holding or connected to a plug 113, which, as it moves with the diaphragm 112, opens and closes a main orifice 114. A bleed orifice 116, in conjunction with the pilot valve plunger 106, controls pressure causing movement of diaphragm 112 so as to open and close the main orifice 114, which when opened allows flow, e.g., of a pressurized medium (such as a reactant gas or other fluid), along a main flow channel (shown by flow paths along conduit 118). In operation, when the solenoid 104 is energized, it moves the plunger 106 and opens the pilot orifice 102, thereby releasing pressure from the pilot chamber 110. This results in higher pressure on the bottom of the diaphragm 112 which is lifted by the line pressure, opening the main orifice 114. When the solenoid 104 is de-energized, the pilot orifice 102 is closed and full line pressure is applied in the pilot chamber 110 through the bleed orifice 116, thereby providing a seating force for tight closure. In this way, the smaller solenoid, plunger, and pilot orifice operate to effectively control the larger main valve structure.
While existing designs may be able to provide desired operational performance, they can nevertheless prove to be overly complex and expensive for some applications. For example, while such designs can provide excellent proportional-control solenoid-type valves able to swiftly and accurately govern even relatively large volumes and high rates of fluid flow using relatively low levels of electrical power (since the valves are aided by the force counterbalancing achieved through the use of the bellows-type coupling), and/or sensitive and precise valve operation by way of the frictionless suspension of broad-area valve members and the counterbalancing of undesirable pressure-generated forces through a correlated pressure-responsive coupling, the bellows and springs used for such valves can increase cost and complexity in a prohibitive manner for some applications.